Data transmission rates of wireless communication systems are becoming very high along with those of wired communication systems. With such a current trend, standardization of a Coordinated MultiPoint (CoMP) transmission/reception method is under way for a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) system, which is a fourth generation mobile communication system.
The CoMP transmission/reception method relates to transmission/reception operations between at least two points (site, cell, base station, distributed antenna, etc.) and at least one terminal, and can be divided into uplink CoMP transmission and downlink CoMP transmission.
Uplink CoMP transmission is a transmission method in which a predetermined terminal transmits a signal to a plurality of points geographically spaced apart from each other, and the plurality of points perform joint-processing of the signal received from the terminal. In uplink CoMP transmission, the terminal does not need to know from which network node the signal has been transmitted, or what kind of processing has been performed on the received signal, and only needs to know what kind of downlink signaling is provided in relation to the uplink transmission. Thus, uplink CoMP transmission can be employed with no significant change in the standard of a wireless interface.
Downlink CoMP transmission is a method in which a plurality of points geographically spaced apart from each other cooperatively transmit a signal to at least one terminal. In 3GPP technical report (TR) 36.814, a downlink CoMP category is divided into joint processing (JP) and coordinated beamforming/coordinated scheduling (CB/CS), and JP is divided again into joint transmission (JT), in which multiple points simultaneously perform physical downlink shared channel (PDSCH) transmission, and dynamic point selection (DPS), in which one point performs PDSCH transmission.
JT uses the concept of distributed antennas in which each transmission point of a CoMP cooperating set can use data. In JT, accurate information on a wireless channel is required, and performance easily varies with delay, an estimation error, and so on.
DPS is a method, where one point of a CoMP cooperating set performs PDSCH transmission at a specific moment. In DPS, a transmission point may dynamically vary, and performance may deteriorate due to feedback delay.
CB/CS is a method, where for only a serving point transmits data to a terminal at a specific moment. Since CB/CS is a passive method for avoiding interference between transmission points, it is not expected to give a large capacity increase. Also, when user scheduling/beamforming requires information exchange between different base stations for cooperation between points corresponding to a CoMP cooperating set, a backhaul may be used for information exchange between the different base stations.
Meanwhile, in the 3GPP LTE Release-8 and Release-9 and LTE-Advanced Release-10 standards, all transmission points generally have different physical cell identities (PCIs). Thus, when the aforementioned transmission methods using multiple points are applied to the standards, transmission using multiple points will be performed in an environment in which respective transmission points have individual cell coverage.
For this reason, the existing standards cannot be applied to a multipoint transmission environment in which a plurality of points belong to the same cell and have the same PCI.